This invention relates to a method and apparatus for bonding two articles and, more particularly, to a method of and apparatus for heat bonding a thermoplastic article to another article such as automotive decorative trim.
Automotive subassemblies often consist of molded plastic pieces to which decorative trim is attached. The trim pieces are often chrome-plated metal strips designed to accent or highlight curves and features of the automobile. The articles to which the chrome trims are attached comprise thermoplastic molded substrates such as window inserts which cover seams in the automotive body or act as weatherproofing.
Previously, the method most commonly used for attaching chrome trim to thermoplastic articles consisted of fastening a post to the trim article, projecting the post through an aperture in the plastic article, and crimping or displacing a portion of the post projecting through the thermoplastic article to prevent withdrawal of the post from the thermoplastic article. Generally, the decorative trim article for such applications is shaped to define a channel on the backside of the trim. Thermoplastic "buttons" are provided which comprise a stem portion with integral discs centered at one end of the stem so as to resemble thumb tacks. The disc portions of the buttons are slidably inserted into the channel of the trim so that the stems of the buttons projects outwardly from the channel. The buttons must be properly positioned along the trim channel to assure that the stems of the buttons are aligned with the precast holes in the thermoplastic article. Generally, this is accomplished by an operator placing tape over the buttons to hold them in their proper place along the trim channel. The trim is aligned with the plastic articles, pressed together so that the stems project through the plastic article, and the stems are displaced or crimped to prevent withdrawal.
There are several disadvantages to this known method. Trim strips having non-uniform widths require different size buttons which must be inserted into the channel of the trim in the proper sequence. In addition, the requirement of multiple-size buttons entails the concurrent need to inventory buttons of various sizes. Considerable operator time is spent in selecting the proper button, comparing the stem diameter to the hole in the plastic article, taping it in place for proper alignment of the two articles, and finally crimping them in position. Another disadvantage of the known method is that the stems are subject to breakage during cold weather due to brittleness.
Lastly, use of the known method frequently results in an uneven backside on the thermoplastic article of the finished trim piece caused by the staking of the stem or the displacement of a portion of the thermoplastic substrate itself. The resulting uneven surface on the backside of the article causes poor adherence of the finished trim piece to the body of the car. Accordingly, such trim pieces must be either reworked, scrapped, or an additional layer of material bonded to its back surface to compensate for the uneven surface.
Accordingly, it is the primary object of the present invention to provide an improved method of an apparatus for bonding two articles. A further object of the present invention is to provide a method by which two articles are bonded without the use of separate fasteners. Another object of the present invention is to provide a method of bonding two articles together which leaves a flat backing surface for subsequent adhesion to an automobile. Yet another object of the present invention is to provide a method for bonding two articles which results in accurate alignment of the two articles after bonding.
The above objects of the present invention are achieved by providing a thermoplastic article and an article with flanges defining a channel and then bonding the two articles together by displacing a portion of the thermoplastic material into the channel of the second article.
According to one embodiment to the present invention, a channel defining surface on the plastic article allows rapid and accurate alignment of the second article with the first article. A controlled flow of hot air is directed at the surface of the thermoplastic material to plasticize a controlled portion thereof. A stake contacts and displaces the plasticized portion of the first article into the channel of the second article. This process results in a greater overlap of displaced material in the bond area than the current processes. Upon return of the thermoplastic material to a rigid state, the two articles are firmly and accurately bonded. Separation forces are distributed by the bond over a wider area, thus reducing the possiblity of separation. Total process cycle time for bonding the two articles is approximately fifteen seconds as opposed to several minutes under the known procedure.
From the subsequent descriptions of the preferred embodiments and the appended claims taken in conjunction with the accompanying drawings, additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates.